<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="author" content="VectorX">
    <meta name="keywords" content="表格的样式">
    <title>表格的样式</title>
    <style>
        .box1 {
            height: 0;
            width: 0;
            border: 10px solid;
            border-color: transparent transparent red transparent;
            border-top: none;
        }
    </style>
</head>

<body>
    <div class="box1"></div>
</body>

</html>